Via plug adapter

ABSTRACT

A circuit includes a substrate having a dielectric layer with a first surface and a second surface. A conductive layer is formed on the first surface. A beveled via is formed in a dielectric layer of the substrate. The via has a first opening of a first width in the first surface, and a second opening of a second width in the second surface, the second width being greater than the first width. A conductive plug is connected to the conductive layer. The plug is formed in the via and extends from adjacent the first opening toward the second opening, and terminates adjacent the second opening at a plug interface surface. A conductive solder ball is connected to the plug interface surface and extends to protrude from the second surface.

BACKGROUND

[0001] The disclosures herein relate generally to solder ball electronicinterconnections and more particularly to a via plug adapter forstrengthening a solder ball connection in a beveled via.

[0002] Vertical interconnects between circuit layers is well known. U.S.Pat. No. 3,541,222 discloses a connector screen for interconnectingaligned electrodes of adjacent circuit boards or modules. The connectorscreen comprises a matrix of spaced conductive connector elementsembedded in a supporting non-conducting material with the conductiveconnector elements protruding from both sides thereof. The size andspacing of the connector elements are chosen so that the connectorscreen can be disposed between the circuit boards or modules to providethe required interconnections between the electrodes without requiringalignment of the connector screen with respect to the boards or modules.A preferred method of making the connector screen involves forming aconductive mold having a grid pattern of ridges in a non-conductivebase. Conductive material is then cast between the ridges of the mold,following which selected portions of the mold are removed to form a webof non-conductive material supporting a matrix of spaced conductingelements protruding from both sides of the web.

[0003] U.S. Pat. No. 4,830,264 describes a method of forming solderterminals for a pinless module, preferably for a pinless metallizedceramic module. The method is comprised of the following steps: forminga substrate having a pattern of conductors formed onto its top surfaceand preformed via-holes extending from the top to bottom surface;applying a droplet of flux at at least one of the preformed via-holeopenings of the bottom surface of the substrate to fill the via-holeswith flux by capillarity and form a glob of flux at the bottom openings;applying a solder preform, i.e. solder balls on each glob of flux towhich it will adhere, the volume of the preform being substantiallyequal to the inner volume of the via-hole plus the volume of the bump tobe formed; heating to cause solder reflow of the solder preform to fillthe via-hole and the inner volume of the eyelet with solder; and,cooling below the melting point of the solder so that the molten soldersolidifies to form solder terminals at the via-hole locations whileforming solder columns in the via-holes. The resultant pinlessmetallized ceramic module has connections between the I/O's of themodule interfacing with the next level of packaging (i.e., printedcircuit boards), that consist of integral solder terminals. Eachintegral solder terminal comprises a column in the vias of themetallized ceramic substrate, a mound of solder at the top surface ofthe substrate and spherical solder bumps on the bottom level for makinginterconnections with the next level of packaging.

[0004] In U.S. Pat. No. 5,401,913, a multi-layer circuit board includeselectrical interconnections between adjacent circuit board layers of themulti-layer board. A via hole is provided through a circuit board layer.The via hole is filled with a via metal. The via metal is plated with alow melting point metal. An adhesive film is deposited over the circuitboard layer. Adjacent layers of the multi-layer circuit board arestacked and aligned together. The layers are laminated under heat andpressure. The low melting point metal provides an electricalinterconnection between adjacent layers.

[0005] U.S. Pat. No. 5,491,303 discloses an interposer for connectingtwo or more printed circuit boards comprising a circuit-carryingsubstrate with two or more solder pads on each of two sides. Each of thesolder pads are connected to an electrically conductive via in thesubstrate, providing electrical interconnection from one side to theother side. Each solder pad has a solder bump on it. A circuit assemblyis made by soldering the solder bumps on one side of the interposer tocorresponding solder pads on a printed circuit board. The solder bumpson the other side of the interposer are likewise soldered to thecorresponding solder pads of a second printed circuit board.

[0006] U.S. Pat. No. 5,600,884 describes an electrical connectingmember, one surface of which is connected to a connecting section of afirst electrical circuit member and another surface of which isconnected to a connecting section of a second electrical circuit member.The electrical connecting member includes a holding member formed of anelectrically insulative member. The holding member has a plurality ofrecess holes. The connecting member also includes a plurality ofelectrically conductive members provided in the electrically insulativemember, insulated from each other. One end of the electricallyconductive members is exposed on one surface of the holding member to beconnected to the connecting section of the first electrical circuitmember. Another end of the electrically conductive members is exposed onanother surface of the holding member to be connected to the connectingsection of the second electrical circuit member.

[0007] U.S. Pat. No. 5,726,497 discloses a method of manufacture of asemiconductor device on a silicon semiconductor substrate whichcomprises formation of a first stress layer on the semiconductorsubstrate, formation of an interconnect layer over the first stresslayer, formation of a second stress layer on the interconnect layer,formation of an inter-metal dielectric (IMD) layer over the secondstress layer, patterning and etching a via opening through theinter-metal dielectric layer and the second stress layer, exposing acontact area on the surface of the metal interconnect layer, and heatingthe device at a temperature sufficient to squeeze the metal interconnectlayer up into the via.

[0008] U.S. Pat. No. 5,757,078 discloses a semiconductor deviceincluding a semiconductor chip having electrode pads, a package composedof a plurality of insulating films and adhered to the semiconductor chipby an adhesive agent. The package includes wiring patterns interposedbetween the plurality of insulating films. The wiring patterns areselectively connected to the electrode pads at one end, and to theplurality of electrically conductive protrusions at the other end, bymeans of via-holes. The semiconductor device further includes aplurality of electrically conductive protrusions extending from theoutermost wiring patterns by way of the via-holes provided in theoutermost insulating film.

[0009] Japanese Application JP 10-41356 discloses a tape carrier that isused as the bonding medium when semiconductor elements are bonded to theouter part of a substrate board for a BGA application. An insulatingfilm includes vias having straight or non-tapered walls. A conductiveland is formed in the vias and solder balls have one side engaged withthe lands inside of the vias. The remainder of each solder ballprotrudes from the insulating film.

[0010] The use of flexible circuitry in IC packaging has been a growingtrend for many years where the use of via connections through theflexible circuit dielectric have been employed in Tape Ball Grid Array(TBGA) IC packaging applications and recently, into Chip Scale Packaging(CSP) applications. In Ball Grid Array (BGA) applications, the viainterconnection traditionally uses a solder ball reflowed first toconnect to the flexible circuitry through the via, then second, reflowedonto the printed circuit board with conventional surface mount assemblypractices.

[0011] This solder ball connection must make a reliable electronicinterconnect from the flexible circuitry to the printed circuit board.This reliability is often directly related to the area of the solderconnection to the flexible circuitry, as a common failure mode of thisinterconnection is the solder ball shearing through the solder materialat the point of the minimum cross sectional area. Therefore, larger viasare desirable to increase the area in which shear stress is distributedto meet minimum solder ball interconnection reliability requirements.

[0012] Conversely, the demand for smaller electronic packages and higherinput/output (I/O's) requires increased routing density, includingsmaller via sizes to allow electronic traces to route between solderball via areas. Smaller vias require smaller via capture pads, thus,allowing more space to route electronic traces between printed circuitboard interconnection vias.

[0013] Traditionally, vias in the dielectric are made by punching,leaving a via through the dielectric with straight walls. Other methodsinclude chemically dissolving the dielectric and laser drilling toexpose the metal conductor of the flexible circuitry. Direct solder ballattachment to any of these via methods controls the solder ballinterconnection reliability by means of the via size, such that, viastypically have to be larger than 0.200 mm in diameter to meet minimumreliability requirements for the electronic package.

[0014] Therefore, what is needed is an apparatus and a method forproviding a strong and reliable solder ball connection to flexiblecircuitry with small diameter vias and via capture pads so as to permitmore space in which to route more electronic traces.

SUMMARY

[0015] One embodiment, accordingly, provides a strength enhanced solderball connection to flexible circuitry with small diameter vias whichimproves the routability of the flexible circuit to address higher I/Oand finer pitch flex based BGA packaging applications. To this end, acircuit comprises a substrate including a dielectric layer having afirst surface and a second surface. A conductive layer is on the firstsurface. A beveled via is formed in the dielectric layer and has a firstopening of a first width in the first surface, and a second opening of asecond width in the second surface, greater than the first width. Aconductive plug is formed in the via, connected to the conductive layer,and extends from adjacent the first opening toward the second opening.The plug terminates adjacent the second opening at a plug interfacesurface. A conductive solder ball is connected to the plug interfacesurface and extends to protrude from the second surface.

[0016] A principal advantage of this embodiment is that the via adapterplug enables a reliable solder ball connection to flexible circuitrywith small (less than 0.200 mm diameter) vias. Using the via plugadapter concept, solder ball interconnection reliability does not haveto be compromised to accommodate the routing requirements of high I/O,fine pitch flex based IC packaging applications. Using common designrules for flexible circuitry, a smaller via allows for a smaller viacapture pad, thus, more space between via capture pads in which to routeelectronic traces.

BRIEF DESCRIPTION OF THE DRAWINGS

[0017]FIG. 1 is a side view illustrating an embodiment of a substrateinterconnected to a circuit board by a plurality of solder balls.

[0018]FIG. 1A is a top view illustrating a circular via opening.

[0019]FIG. 1B is a top view illustrating an oblong via opening.

[0020]FIG. 2 is a side view illustrating an embodiment of a plug in atapered via.

[0021]FIG. 3 is another side view illustrating an embodiment of a plugin a tapered via.

[0022]FIG. 4 is another side view illustrating an embodiment of a plugin a tapered via.

[0023]FIG. 5 is a side view illustrating an embodiment of a substrateinterconnected to a circuit board by a solder ball.

[0024]FIG. 6 is a side view illustrating an embodiment of a two-layeredsubstrate interconnected to a circuit board by solder ball.

[0025]FIG. 7 is a side view illustrating an embodiment of a chip scalepackage including an IC chip connected to a substrate.

[0026]FIG. 8 is a view of the substrate taken along line 8-8 of FIG. 7.

DETAILED DESCRIPTION

[0027] According to one embodiment, FIG. 1, a flexible circuit 10comprises a substrate 12 formed of a flexible dielectric material. Thesubstrate 12 is of a polymer or other suitable material having athickness T1 of from about 0.5 mils to about 5.0 mils. The polymer maybe a polyimide, a polyester, or other known polymers for electronicapplications. Substrate 12 also includes a first surface 14 and a secondopposite surface 16. A conductive layer 18, of copper, gold platedcopper, gold or other suitable material, is formed on first surface 14and includes a plurality of conductive capture pads 20 and a pluralityof conductive traces 22 routed between the capture pads 20.

[0028] A plurality of beveled vias 24 are formed in substrate 12. Eachvia 24 has a first opening 26 of a first width W1, in first surface 14,and a second opening 28 of a second width W2, in the second surface 16.Second width W2 is greater than first width W1. Beveled via 24 includesa sidewall 30 which is sloped away from first surface 14 at an angle αof from about 20 degrees to about 80 degrees, and preferably at an angleof from about 20 degrees to about 45 degrees. First opening 26 iscircular, FIG. 1A, or oblong, FIG. 1B or may be of another suitableshape and first width W1 is from about 0.05 mm to about 0.5 mm.

[0029] A conductive plug 32, FIGS. 1 and 2 is formed in beveled via 24,and extends from a first plug interface surface 34, adjacent firstopening 26, toward the second opening 28. Plug 32 terminates adjacentthe second opening 28 at a second plug interface surface 36. The firstplug interface surface 34 is connected to conductive capture pad 20. Thesecond plug interface surface 36 is of a dome shape. Second pluginterface surface 36 may be formed to terminate between first surface 14and second surface 16, may be formed such that a portion of the domeextends outwardly from the second surface 16, FIG. 3, or may be formedsuch that the entire dome-like surface extends outwardly from the secondsurface 16, FIG. 4. Thus, a range of plug thickness or height T2extending from first plug interface surface 34 to second plug interfacesurface 36 may vary, but is at least 5 microns, FIG. 2.

[0030] A conductive solder ball 38, FIG. 5, is connected to second pluginterface surface 36 at a first solder ball surface 40, and protrudesfrom second substrate surface 16. Solder ball 38 terminates at a secondsolder ball surface 42 which may engage a printed circuit board 44. Plug32 and solder ball 38 may be formed of various suitable materials. Forexample, plug 32 may be formed of a high temperature tin-lead solderengaged with solder ball 38 formed of a eutectic tin-lead solder. Also,plug 32 may be formed of copper engaged with solder ball 38 formed of atin-lead solder. Other combinations may be used which meet theconductivity requirement and meet the condition that they provide theplug material of a stronger shear strength than the solder ballmaterial. As a further example, plug 32 may be formed of nickel engagedwith solder ball 38 formed of a tin-lead solder. In addition, forimproved bonding, an interface coating 46 may be provided betweencapture pads 20 and first plug interface surface 34. Coating 46 may beformed of a suitable material selected from gold, paladium andnickel-gold. Furthermore, bonding between plug 32 and solder ball 38 maybe improved by another interface coating 48 therebetween. Coating 48 maybe formed of a suitable material also selected from gold, paladium andnickel-gold.

[0031] Beveled vias 24, FIG. 1, are spaced apart in a side-by-sideconfiguration. Capture pads 20 are formed at each first opening 26.Therefore, capture pads 20 are also spaced apart in a side-by-sideconfiguration. Spacing between vias 24 is of a center-to-center distanceD of from about 0.25 mm to about 1.27 mm. This spacing permits at leastthree traces 22 to pass between side-by-side capture pads 20.

[0032] In FIG. 6, circuit 10 includes a substrate including a firstdielectric layer 12 a and a second dielectric layer 13. First dielectriclayer 12 a includes a first surface 14 a and a second surface 16 a. Aconductive layer 18 a is provided on first surface 14 a between firstdielectric layer 12 a and second dielectric layer 13. A beveled via 24is formed in first dielectric layer 12 a as described and referred toabove. Also, the second dielectric layer 13 may be formed of a polymermaterial as described above. One of the layers 12 a and 13 may beprovided as a cover coat for the other layer.

[0033] Well known tape ball grid array (TBGA) package typically includesa substrate having an integrated circuit (IC) mounted in a cavity thatis surrounded by an array of vias. Leads from the IC interconnect to thevias. One embodiment herein, FIGS. 7 and 8, discloses a substantialimprovement such that the substrate is substantially of the same surfacearea as the IC. This is possible due to the reduced size openings of thetapered vias as described above. Thus, the advantages provided by thereduced size openings permits increased trace routing between the vias.Also, the opposite or larger via openings provide increased surfacecontact to improve solder ball shear strength. The chip scale package100, FIG. 7, includes a substrate 112 having a first surface 114 and asecond surface 116. A surface area A1 of first surface 114 issubstantially the same as a second surface area A2 of an IC 150 mountedon substrate 112. A conductive layer 118 on portions of first surface114 area is connected to IC 150 by leads 152. An adhesive layer 155 onsurface 114 of substrate 112, and an adhesive layer 157 on IC 150 areinterconnected by an interposer layer 154 therebetween. The interposerlayer 154 may, for example, be a compliant material such as a foam orelastomeric material, or a non-compliant material such as a ceramic or acopper sheet. Substrate 112 includes a plurality of beveled vias 124, asdescribed above. Each via includes a first opening 126 in first surface114 and a second opening 128 in second surface 116. The second widthbeing greater than the first width as herein described. A plug 132 isprovided in each via to extend from adjacent the first opening 126 toadjacent the second opening 128 and terminating at a plug interfacesurface 136. A conductive solder ball 138 is connected to the pluginterface surface 136 and extends to protrude from second surface 116for connection to a printed circuit board 144. Thus, a plurality ofsolder balls 138 provide an array which is uniform across second surface116 of substrate 112, without interruption by a commonly heretoforeknown space required for mounting an IC package on opposite surface 114.

[0034] As it can be seen, the principal advantages of these embodimentsare that the via plug adapter enables a reliable solder ball connectionto flexible circuitry with small (less than 0.200 mm diameter) vias.Using the via plug adapter concept, solder ball interconnectionreliability does not have to be compromised to accommodate the routingrequirements of high I/O, fine pitch flex based IC packagingapplications. Using common design rules for flexible circuitry, asmaller via allows for a smaller via capture pad, thus, more spacebetween via capture pads in which to route electronic traces. As anexample, using a via plug adapter in a 0.085 mm diameter beveled via, 4traces can be routed between capture pads with similar solder ballinterconnection reliability as with 0.300 mm diameter vias that onlyallow routing of a single trace.

[0035] The foregoing describes a flexible circuit with a z-axis viainterconnection between fine feature flexible circuitry and grossfeature printed circuit board solder ball pads using traditional solderballs with the novel use of a via plug adapter. One such application ofthis via plug adapter is the flexible circuit application in ICpackaging for BGA to printed circuit board interconnection.

[0036] The via plug adapter is a metal plug additively plated into abeveled via. In addition to forming the plug using an additive platingprocess, a process such as solder reflow could be used to form the viaplug. This via plug adapter is a frustum (the solid of a cone betweentwo parallel planes) shaped metal feature with a slight dome shape atthe second interface surface. As the z-direction thickness of thefrustum grows within the beveled via, the surface area for traditionalsolder ball attachment grows dramatically creating a mechanical adapterallowing small vias to have similar solder ball interconnectionreliability as with large via applications.

[0037] Allowing small vias in the flexible circuit improves theroutability of the flexible circuit to address higher 1/0 and finerpitch flex based BGA packaging applications.

[0038] As a result, one embodiment provides a circuit comprising asubstrate including a dielectric layer having a first surface and asecond surface. A conductive layer is on the first surface. A beveledvia is formed in the dielectric layer. The via has a first opening of afirst width in the first surface and a second opening of a second width,in the second surface, greater than the first width. A conductive plugis connected to the conductive layer and is formed in the via andextends from adjacent the first opening toward the second opening. Theplug terminates adjacent the second opening at a plug interface surface.A conductive solder ball is connected to the plug interface surface, andextends to protrude from the second surface.

[0039] Another embodiment provides a circuit comprising a substrateincluding a dielectric layer having a first surface and a secondsurface. A conducted layer is on the first surface. A beveled via isformed in the dielectric layer. The via has a first opening of a firstwidth in the first surface and a second opening of a second width in thesecond surface, greater than the first width. A conductive plug isconnected to the conductive layer and is formed in the via and extendsfrom adjacent the first opening toward the second opening. The plugterminates adjacent the second opening at a plug interface surface. Aconductive solder ball has a first solder ball surface connected to theplug interface surface. The solder ball extends to protrude from thesecond surface and terminates at a second solder ball surface. A printedcircuit board is engaged with the second solder ball surface.

[0040] In still another embodiment, a circuit comprises a substrateincluding a dielectric layer having a first surface and a secondsurface. A pair of side-by-side beveled vias are formed in thedielectric layer. Each via has a first opening of a first width in thefirst surface, and a second opening of a second width in the secondsurface, greater than the first width. Each via includes a conductiveplug having a first plug interface surface adjacent the first opening.Each plug extends from adjacent the first plug interface surface towardthe second opening. Each plug terminates adjacent the second opening ata second plug interface surface. A conductive solder ball is formed ateach via and has a first solder ball surface engaged with its respectivesecond plug interface surface, and extends to protrude from the secondsurface. Each solder ball terminates at a second solder ball surface. Aprinted circuit board is engaged with the second solder ball surface. Aconductive capture pad layer is engaged with the first interface surfaceof each plug to form side-by-side, spaced apart, capture pad layers. Aplurality of conductive traces extend between the side-by-side capturepad layers.

[0041] A further embodiment provides a method of attaching a solder ballto a via in a flexible circuit substrate. This is accomplished byforming a beveled via in the flexible circuit substrate having a firstsurface and a second surface. A first via opening is formed in the firstsurface and has a first width. A second via opening is formed in thesecond surface and has a second width, greater than the first width. Aconductive layer is formed at the first opening. A conductive plug isformed in the beveled via connected to the conductive layer so that theplug extends from adjacent the first surface toward the second surface.The plug terminates at a plug interface surface adjacent the secondsurface. A conductive solder ball is engaged with the plug interfacesurface. The solder ball extends to protrude from the second surface.

[0042] Although illustrative embodiments have been shown and described,a wide range of modifications, change and substitution is contemplatedin the foregoing disclosure and in some instances, some features of theembodiments may be employed without a corresponding use of otherfeatures. Accordingly, it is appropriate that the appended claims beconstrued broadly and in a manner consistent with the scope of theembodiments disclosed herein.

What is claimed is:
 1. A circuit comprising: a substrate including adielectric layer having a first surface and a second surface; aconductive layer on the first surface; a beveled via formed in thedielectric layer, the via having a first opening of a first width in thefirst surface, and a second opening of a second width in the secondsurface, the second width being greater than the first width; aconductive plug connected to the conductive layer, the plug being formedin the via, and extending from adjacent the first opening toward thesecond opening, and terminating adjacent the second opening at a pluginterface surface; and a conductive solder ball connected to the pluginterface surface and extending to protrude from the second surface. 2.The circuit as defined in claim 1 wherein the dielectric layer andconductive layer form a flexible circuit.
 3. The circuit as defined inclaim 2 wherein the dielectric layer is formed of a polymer material. 4.The circuit as defined in claim 3 wherein the polymer material ispolyimide.
 5. The circuit as defined in claim 4 wherein the polymermaterial has a thickness of from about 0.5 mils to about 5.0 mils. 6.The circuit as defined in claim 3 wherein the polymer material is apolyester.
 7. The circuit as defined in claim 2 wherein the beveled viahas a sidewall sloped away from the first surface at an angle of fromabout 20 degrees to about 80 degrees.
 8. The circuit as defined in claim2 wherein the beveled via has a sidewall sloped away from the firstsurface at an angle of from about 20 degrees to about 45 degrees.
 9. Thecircuit as defined in claim 2 wherein the first opening is circular. 10.The circuit as defined in claim 2 wherein the first opening is oblong.11. The circuit as defined in claim 9 wherein the first width is fromabout 0.05 mm to about 0.5 mm.
 12. The circuit as defined in claim 2wherein the plug interface surface forms a dome.
 13. The circuit asdefined in claim 12 wherein the dome is between the first surface andthe second surface.
 14. The circuit as defined in claim 12 wherein aportion of the dome extends outwardly from the second surface.
 15. Thecircuit as defined in claim 12 wherein the entire dome extends outwardlyfrom the second surface.
 16. The circuit as defined in claim 2 whereinthe plug has a thickness dimension extending from the first surface tothe dome, the thickness dimension being at least 5 microns.
 17. Thecircuit as defined in claim 2 wherein the plug is formed of a hightemperature tin-lead solder, and the solder ball is formed of a eutectictin-lead solder.
 18. The circuit as defined in claim 2 wherein the ballis formed of a tin-lead solder and the plug is formed of copper and hasa stronger shear strength than the tin-lead solder.
 19. The circuit asdefined in claim 2 wherein the ball is formed of a tin-lead solder andthe plug is formed of nickel and has a stronger shear strength than thetin-lead solder.
 20. The circuit as defined in claim 2 wherein theconductive layer is formed of copper.
 21. The circuit as defined inclaim 2 wherein the conductive layer is formed of gold plated copper.22. The circuit as defined in claim 2 wherein the conductive layer isformed of gold.
 23. The circuit as defined in claim 20 furthercomprising: an interface coating between the conductive layer and theplug, the coating being selected from the group consisting of gold,paladium and nickel-gold.
 24. The circuit as defined in claim 23 furthercomprising: an interface coating between the interface surface of theplug and the ball, the coating being selected from the group consistingof gold, paladium and nickel-gold.
 25. A circuit comprising: a substrateincluding a dielectric layer having a first surface and a secondsurface; a conductive layer on the first surface; a beveled via formedin the dielectric layer, the via having a first opening of a first widthin the first surface, and a second opening of a second width in thesecond surface, the second width being greater than the first width; aconductive plug connected to the conductive layer, the plug being formedin the via and extending from adjacent the first opening toward thesecond opening, and terminating adjacent the second opening at a pluginterface surface; a conductive solder ball having a first solder ballsurface connected to the plug interface surface, and extending toprotrude from the second surface, the solder ball terminating at asecond solder ball surface; and a printed circuit board engaged with thesecond solder ball surface.
 26. A circuit comprising: a substrateincluding a dielectric layer having a first surface and a secondsurface; a pair of side-by-side beveled vias formed in the dielectriclayer, each via having a first opening of a first width in the firstsurface and a second opening of a second width in the second surface,the second width being greater than the first width; each via includinga conductive plug having a first plug interface surface adjacent thefirst opening, each plug extending from adjacent the first pluginterface toward the second opening, each plug terminating adjacent thesecond opening at a second plug interface surface; a conductive solderball formed at each via, each solder ball having a first solder ballsurface engaged with its respective second plug interface surface, andextending to protrude from the second surface, each solder ballterminating at a second solder ball surface; a printed circuit boardengaged with the second solder ball surface; a conductive capture padlayer engaged with the first interface surface of each plug to formside-by-side, spaced apart capture pad layers; and a plurality ofconductive traces extending between the side-by-side capture pad layers.27. The circuit as defined in claim 26 wherein the first width is fromabout 0.05 mm to about 0.5 mm.
 28. The circuit as defined in claim 27wherein the pair of side-by-side beveled vias have a center-to-centerdistance therebetween of from about 0.25 mm to about 1.27 mm.
 29. Thecircuit as defined in claim 28 wherein the plurality of conductivetraces includes at least three traces.
 30. A method of attaching asolder ball to a via in a flexible circuit substrate comprising thesteps of: forming a beveled via in the flexible substrate, the substratehaving a first surface and a second surface; forming a first opening ofthe via in the first surface having a first width, and forming a secondopening of the via in the second surface having a second width, greaterthan the first width; forming a conductive layer at the first opening;forming a conductive plug in the beveled via connected to the conductivelayer so that the plug extends from adjacent the first surface towardthe second surface; terminating the plug at a plug interface surfaceadjacent the second surface; forming a conductive solder ball engagedwith the plug interface surface; and extending the solder ball toprotrude from the second surface.
 31. A circuit comprising: a substrateincluding a first dielectric layer and a second dielectric layer, thefirst dielectric layer having a first surface and a second surface; aconductive layer on the first surface, between the first and seconddielectric layers; a beveled via formed in the first dielectric layer,the via having a first opening of a first width in the first surface,and a second opening of a second width in the second surface, the secondwidth being greater than the first width; a conductive plug connected tothe conductive layer, the plug being formed in the via, and extendingfrom adjacent the first opening toward the second opening andterminating adjacent the second opening at a plug interface surface; anda conductive solder ball connected to the plug interface surface andextending to protrude from the second surface.
 32. A chip scale packagecomprising: a substrate including a dielectric layer having a firstsurface of a first surface area and a second surface; a conductive layeron portions of the first surface area; an integrated circuit mounted onthe first surface area, the integrated circuit having a surface areasubstantially the same size as the first surface area, the integratedcircuit being electrically connected to the conductive layer; an arrayof beveled vias formed in the dielectric layer, each via having anopening of a first width in the first surface, and a second opening of asecond width in the second surface, the second width being greater thanthe first width; a conductive plug formed in the vias and connected tothe conductive layer, the plug extending from adjacent the first openingtoward the second opening, and terminating adjacent the second openingat a plug interface surface; and a conductive solder ball connected tothe plug interface surface and extending to protrude from the secondsurface.